Electrode structure for image-reproducing cathode-ray tubes



Nov. 27, 1956 J. E. BYRNE 2,772,375

ELECTRODE STRUCTURE FOR IMAGE-REPRODUCING CATHODE-RAY TUBES Filed Jan. 14, 1954 2 Sheets-Sheet l 5 uvmwon.

Joseph 5 [By/we HGE/UT wi-iii-liwHwflllllllll y NOV. 27, J. E. BYRNE ELECTRODE STRUCTURE FOR IMAGEFREPRODUCING CATHODE-RAY TUBES Filed Jan. 14, 1954 2 Sheets-Sheet 2 26 INVENTOR. Joseph E B y/We United States Patent ELECTRODE STRUCTURE FOR IMAGE-REPRO- DUClNG CATHODE-RAY TUBES Joseph E. Byrne, Lafayette, Calif., assignor to Chromatic Television Laboratories, Inc., New York, N. Y., a corporation of California Application January 14, 1954, Serial No. 403,987

6 Claims. (Cl. 313-78) The present invention relates to electrode structures for cathode-ray tubes. More particularly, it relates to an electrode structure for cathode-ray tubes which is adapted to bring about a change in the color reproduced thereby through an auxiliary, or micro-, deflection of the cathoderay beam in the vicinity of the target.

In Letters Patent of the United States No. 2,692,532 granted to Ernest 0. Lawrence, on October 26, 1954, there is set forth a cathode-ray tube having a grid structure of parallel wires located adjacent to a colored phosphor screen. One function of this structure is to focus the beam electrons into a pattern of thin lines nominally registered with discrete phosphor areas of the target.

In the above-referred-to Lawrence patent, the cathode ray tube is designed with a relatively large number of narrow component-color phosphor strips laid down in a predetermined sequence to form a target electrode. These phosphor strips luminesce, when impacted by the cathode ray beam, in various component colors of the image to be synthesized, such, for example, as red, green and blue. A conductive coating overlies these phosphor strips.

In order to bring about the phenomenon known as post-deflection-focusing, the path of an electron directed to the phosphor screen from the cathode emitter of the tube is controlled in a selective manner in the vicinity of the target. This is accomplished by means of a grid assembly located adjacent to the phosphor screen. Such a grid assembly, in conjunction with the phosphor screen, may comprise a unitary electrode structure of the type to which the present invention is particularly applicable.

A grid of the above nature may be formed of a large number of coplanar wires, or linear conductors, extending in the same direction as the phosphor strips, and lying in the path of the electrons directed to the target electrode from the electron gun of the cathode-ray tube. When a cathode-ray tube of the type having a single electron gun is employed, the order or sequence in which the phosphor strips of the target are laid down may be red, green, blue, green, red, green, etc., bearing in mind that the color of a phosphor, as used herein, refers to the color of the light emitted therefrom which reaches the eye of an observer. in such a case, the wires of the grid assembly are electron-optically related to the phosphor strips, so that, in this electron-optical sense, there is a wire aligned with each blue strip, and similarly 'a wire aligned with each red" strip. All of the wires associated with the red" strips are connected to a common terminal, while the blue WilCS are similarly joined together electrically.

It now a difference of potential is established between the plane of the wire grid assembly and the conductive coating on the phosphor strips, a series of converging electrostatic fields for the beam electrons is created. When the magnitude and polarity of this potential difference is properly chosen, the converging fields will cause the beam electrons arriving at the wire grid from the electron gun of the tube to form a fine line structure on the phosphor target.

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Inasmuch as the grid wires are electron-optically aligned with the phosphor strips, a zero difference of potential between the red and blue terminals of the grid will result in the beam electrons undergoing this focusing action alone. Accordingly, the electrons may be caused to impinge the target within the boundaries of a particular strip such as green. If the wires or conductors associated with the red strips are now made positive relative to the conductors electron-optically related to the blue strips, the beam electrons will be subjected to an auxiliary, or micro-, deflection in addition to the deflection providing the raster, so that the lines of impingement of the electrons will now lie within the respective boundaries of the red strips. Similarly, electrons will strike the blue phosphor areas when the wires associated therewith are suitably positive with respect to the red wires. It will now be appreciated that the particular component color of the image displayed at any instant of time will be in accordance with the potential difference (if any) existing between the two sections of the grid wire assembly.

Various methods are now known for constructing color grid structures which produce these results. One preferred design is set forth by Letters Patent of the United States No. 2,683,833 granted to Renn Zaphiropoulos on July 13, 1954. The essential feature of the Zaphiropoulos arrangement is that the glass plate carrying the phosphor strips is sandwhiched between the wires of the grid, on one hand, and one or more frame portions to which the wires are attached, on the other. Consequently, the tension of the grid wires exerts a pressure upon the glass plate, and this pressure acts to hold the frames, plate and wires in a unitary assembly.

Although the above-described Zaphiropoulos structure is completely satisfactory insofar as operation is concerned, and produces an image in which there is substantially no color contamination, nevertheless it is somewhat time-consuming to manufacture due to the techniques employed. As presently constructed, each set of grid wires is attached to a frame section by hooking a continuous wire around a projection on the frame, laying down the wire across the raster area of the base plate, hooking it over a projection on the opposite side of the same frame section, bringing it back across the raster area of the base plate, and so on. A winding operation is thus carried out which, while producing a grid of satisfactory operating characteristics, nonetheless requires a considerable amount of time to complete and hence materially reduces the number of color grid structures that may be manufactured in a given period. To overcome this difiiculty, the same Zaphiropoulos application illustrates an alternative method of grid design in which the wires are continuously wound around the base plate in coil-like fashion so as to eliminate the above-described back-and-forth motion. However, this leaves a set of Wires on the rear, or viewing side, of the base plate which have to be removed prior to operation of the tube. Furthermore, the wires must be cemented in position before they are cut, and this introduces the possibility that the wires may become loose and interfere with image reproduction.

In a further copending United States patent application of Ernest 0. Lawrence, Serial No. 234,190 filed June 29, 1951, there is disclosed a cathode-ray tube of the type in which the color-reproducing cycle is such that the particular color instantaneously displayed is dependent upon the angle of incidence of the cathode-ray beam atthe plane of the grid wires. There is no auxiliary, or micro, deflection produced by the grid assembly, and all of the wires of this grid may be maintained at the same potential relative to the conductive coating on the phosphor screen. As a result of this potential difference, and with proper spacing between the grid assembly and the screen, all of the electrons passing between any adjacent pair of wires are brought to a focus area of smaller width than the wire spacing.

Since there is no necessity for dividing the grid of the above-mentioned Lawrence application into electrically insulated sections, it is possible to employ that form of construction set forth in a concurrently filed United States patent application of Leslie J. Cook and Lawrence T. Quaglia, Serial No. 404,038, entitled Grid Structure for Cathode-Ray Tubes Designed for Polychrome Image Reproduction. According to a feature of this last-mentioned Cook et al. application, a substantially rectangular grid frame is employed around which a continuous conductor is wound in an uninterrupted fashion. This results in two sets, or groups, of parallel wires which lie in different planes. However, means are further provided for applying pressure to the strand conductors of each of these sets relative to the other to cause each such strand to assume a position wherein both sets of wires are essentially coplanar. Inasmuch as this design does not comprehend a direct physical connection between the wire strands and the glass base plate on which the colored phosphor strips are deposited, these two members are brought into juxtaposition so that all of the coplanar wire strands are respectively indexed in notches in a pair of spacer bars carried by the glass plate. When the plate (and its support) are secured to the grid frame, then the entire assembly becomes in eifect a unitary structure.

The continuously wound type of grid wire assembly set forth in this Cook et al. application embodies many desirable features, and permits manufacturing of the grid to be carried out by simple mechanical means at a relatively low cost. However, it is obvious that one of the characteristics of such a design is that it is directed to a multiple-gun cathode-ray tube in which the color produced is dependent upon the angle of incidence of the cathoderay beam as it arrives at the grid from the main deflection area of the cathode-ray tube. There is no means for separating the strand conductors into two separate groups so that different potentials may be applied thereto in order to permit a micro-deflection of the scanning beam. This is due to the fact that the grid wires are all wound upon a single frame which in itself is electrically conductive, and, in addition, the wire strands are maintained in coplanar relationship by pressure applied through a pair of bars which are composed of metal or some other electrically conductive substance. It would be highly desirable to retain the basic advantages of the structure set forth by Cook and Quaglia (insofar as its ease of construction and adaptability to mass production is concerned) and at the same time adapt it for use with a single-gun cathoderay tube in which the wire grid acts as a color deflector.

To produce such a design a proposal has been made to utilize two rectangular frame sections which are employed instead of the single frame section utilized in the Cook et al. structure. These two frame sections of the last proposed construction may be of the same general configuration and are intended for positioning side-by-side, in which position they may be riveted or otherwise secured together. One of these two frame sections, which may be termed an upper frame section, is adapted to have a continuous conductor wound around it in the same manner as disclosed by Cook et al. However, the winding operation is such that the individual wires are not only offset but also spaced further apart than they are in the Cook et al. arrangement. A further conductor is wound around the other, or lower, frame section in similar fashion-that is, with the same wire spacing as that used for the first winding. The two frame sections are then brought into position so that the wire strands associated with one frame section are shifted laterally with respect to the wires associated with the other, or in other words so that each individual wire strand wound around the upper frame section lies between two individual, wire strands. of

4 the lower frame section. This results in a grid having the same number of individual wires as set forth by Cook and Quaglia except that the wires now lie in more than two planes.

To separate electrically one set of wires from the other, a layer of electrically insulating material (which in one example may be glass tape) is inserted between the two frame sections before they are brought into face-to-face relation. Thus there is no electrical contact between the upper frame section and its wires, on one hand, and the lower frame section and its associated wires, on the other. Two pairs of insulating rods, which may be of glass or other ceramic composition, are then employed to compress both the upper and lower groups of wires to a position in which all the wire strands are substantially c0- planar.

It has been stated above that the use can be made of two individual frame sections each of which is associated with that particular group of Wires which are adapted to be electrically connected together. As preferably constructed, each of these frame sections is Wound in continuous fashion, and then the two frame sections brought together side-by-side with some form of intermediate insulation so as to preclude electrical contact between one frame section and the other. Following this operation, two frame sections are secured together by rivets or other binding means. It will be recalled that although Cook and Quaglia illustrate but a single frame section, their disclosure is for use with a multiple-gun tube in which there is no microdeflection by the grid, and in which the color produced is dependent upon the angle of incidence of the cathode-ray beam at the plane of the wire grid assembly.

In accordance with a principal feature of the present invention, a single rectangular frame section is employed around which a continuous conductor is wound in coillike fashion. The spacing between adjacent strand conductors is twice the spacing desired between wires of the finished grid. Following this first winding operation, a layer of electrically insulating material, which may be of any suitable composition such, for example, as glass tape, is placed over the sides of the frame around which the continuous conductor is wound. A second continuous conductor is then wound over this insulating layer in such a manner that each turn of the second winding lies between adjacent strand conductors of the first winding. When completed, there will be two sets of grid wires which are interleaved with one another, and which are electrically separate due to the insulating layer between the windings. However, the wires will lie in four separate planes due in part to the thickness of the insulation laid upon the first set of conductors as they pass over the frame. If, then, two pairs of insulating bars are employed to apply pressure to the sets of wires, all of the four sets of wires will be brought into substantially coplanar relationship. While achieving similar resultsthat is, producing two wire groups in which alternate strands are electrically connected together with adjacent wires being insulated from one another, nevertheless the actual construction of the wire grid assembly is considerably simplified and is adapted.

to be carried out in shorter time and lower cost. It results in the saving of one frame section and requires the addition of only two strips of insulating material at the two sides of the frame around which the Wires are wound. Consequently, it is highly adaptable to mass production techniques, and is presently being contemplated for use in the quantity manufacture of cathode-ray tubes adapted for polychrome image reproduction.

One object of the present invention, therefore, is to provide an improved type of cathode-ray tube designed for the reconstitution of polychrome images.

A further object of the present invention is to provide a grid structure for cathode-ray tubes, designed especially but not exclusively for polychrome image reproduction.

in which electrically separate portions of the grid may be wound upon a single frame or support,

An additional object of the invention is to provide a method of manufacturing such a grid structure.

A further object of the present invention is to provide a grid structure for cathode-ray tubes, designed especially but not exclusively for polychrome image reproduction, in which a portion of the strand conductors of the grid are wound upon a frame section, strips of insulating material laid upon that portion of the frame section around which the conductors are wound, and then a second set of conductors wound around the same frame section and over the strips of insulating material, thus effectively isolating electrically one set of Wires from the other.

Other objects and advantages of the present invention will be apparent from the following description and from the drawings, in which:

Figure 1 is a semi-diagrammatic view of a cathode-ray tube, showing in cross-section a color grid structure in accordance with the present invention;

Figure 2 is a plan view of the color grid structure of Fig. 1 as seen from the electron gun end of the cathoderay tube;

Figure 3 is a detailed view of a portion of Fig. 2;

Figure 4 is a sectional view of Fig. 3 along the line 44;

Figure 5 is a detailed view of a portion of Fig. 1, showing more clearly the relationship between the wire grid assembly and the glass plate; and

Figure 6 is a plan view of a portion of the target area of Fig. 2, showing one preferred relationship between the grid wires and the phosphor strips.

Referring now to the drawing, there is shown in Fig. l a cathode-ray tube certain parts of which are conventional. For example, in the neck end of the tube, and within the envelope 10, there is an indirectly-heated cathode 12 which acts as a source of electrons for development into a scanning beam. The latter is indicated schematically by the trace 14. Adjacent to, and partially surrounding, the cathode 12 is a control grid #1, or electrode, 16 suitably apertured to permit the passage of electrons which are subsequently formed into the beam 14. The control grid 16 functions in the usual manner to modulate the emitted stream of electrons in accordance with the potential applied thereto relative to the cathode 12. Also in the neck of the tube there is provided a first anode or grid #2 (identified by the reference numeral 18) to which suitable potentials may be applied so as to result in an initial acceleration of electrons emitted from the cathode 12. Adjacent to grid #2 there is positioned a second anode =or grid #3 (reference numeral 20) for applying an additional acceleration to the electrons.

Defiecting coils, comprising a horizontal pair 22 and a vertical pair 24, are provided for the usual scanning purposes. Obviously, the terms horizontal and vertical are used herein in a descriptive sense only. Thus the electron beam 14 is caused to scan a phosphor-coated target, or translucent base plate, 26 to produce light which is visible through the end wall 28 of the envelope 10.

Shown in Fig. 2 is a rectangular support or frame 30 adapted to fit within the envelope of the cathode-ray tube. This frame 30 is made up of a pair of oppositelydisposed members 32, which form two sides of the frame, and a pair of members 34 which form the remaining two sides. The frame 39 may be fabricated for example, from .062 thick type 430 stainless steel sheet. The members 32 and 34 may thus be integrally formed as best shown in Fig. 3 of the drawings. However, the particular manner of constructing the frame 30 forms no part of the present invention.

The frame 30 is provided at each corner with a lug, or tab, 38 which is shown in Fig. 2 as having a contour generally similar to the internal periphery of the envelope 10. In the case of a metal envelope 10, small angles 40 may be welded to the inside surface of the envelope at positions to which it is desired to attach the lugs 38. The lugs are joined to the angles by means of bolts or rivets 42 which preferably pass through ceramic bushings (not shown) which are provided with insulating discs on each end to isolate electrically the frame 30 from the envelope 10. Other means of attachment may be employed, especially when glass instead of metal envelopes are used. However, since these constructional features form no part of the present invention, and furthermore are mentioned in the abovereferred-to Zaphiropoulos application, no further details: in regard thereto will be set forth herein.

A continuous filamentary conductor (such as #302 stainless steel of .006" thickness) is wound around the oppositely-disposed frame side members 34 in coil-like fashion so as to form two set of strands. One such set of strands (indicated in the drawing by the reference numeral 44) is composed of those which pass over the upper surface of each side member 34 (as best shown in the left hand portion of Fig. 3) and the other set of strands (identified as 46) is composed of those passing along the under surface of the side members. it will be apparent from a consideration of the drawing, and especially from Figs. 4 and 5, that these two sets of strand conductors 44 and 46 will normally lie in separate planes one above the other, the distance between the planes being determined by the thickness of the members 34.

In order that the strand conductors of the above-described first winding operation shall. be substantially equally spaced apart, in a manner best shown in Fig. 3 of the drawings, it is necessary that. the wires of one set, such as 44, be offset with respect to the conductors of the other set 46. One method of accomplishing this is by forming a series of grooves 47 in the outer edge of each of the side members 34. Obviously, if these grooves 47 are so aligned as to be perpendicular, or normal, to the respective planes of the strand conductors 44 and 46 which extend between the members 34 and across the window area of the frame 30, then the corresponding wires of the two sets of conductors will be positioned one above the other. Consequently, the strand conductors of the two groups 44 and 4d are caused to be offset by means of a properly chosen directional alignment of the grooves 47 cut into the side members 34. This alignment is so selected that, when a particular arriving wire strand is looped around the outer edge of one of the side members 34, this looping operation results in the returning strand lying midway between two adjacent wires of the arriving set, considered in a direction normal to the plane of the wires. Expressed diiferently, these grooves are cut into the outer edge of each of the side members 34 in a predetermined direction which is other than normal to the plane of the grid wires. The particular angle at which the grooves 47 are cut will depend at least in part upon the thickness of the frame member 34, but in any event will be so chosen that the returning wires, following their looping around the edge of a member 34, respectively lie midway between the approaching wires of the grid, considered again in a direction normal to the plane of the wires.

Following the above-described first winding operation, a layer of insulating material, indentified in the drawing by the reference numeral 48, is laid over each of the side members 34 of the frame 30. This insulation 48, which may, for example, be glass tape, overlies both the upper and lower surfaces of each of the members 34, as well as the strand conductors 44 and 46 carried thereon as a result of the first winding operation above described. A further winding operation is then carried out which may be similar in many respects to the first winding operation-that is, a second continuous filamentary conductor of the same nature as the first mentioned conductor is wound around the frame members 34 and over the insulation 48. This second winding operation, however, is so effected that each turn of the coil produced thereby falls between adja cent turns of the first winding operation. That is, the second winding will form two further sets of conductors 50 and 52, with the conductors 50 constituting the arriving set (corresponding to the conductors 44 of the first winding operation) and the conductors 52 constituting the returning set (corresponding to the conductors 46 of the first winding operation). As will be best seen from a consideration of Fig. 3 of the drawings the fact that the second winding operation results in a coil the individual strand conductors which are offset with respect to the conductors of the coil formed by the first winding operation, produces a final grid assembly in which all of the strands are substantially equally-spaced apart as best shown in the right hand portion of Fig. 3, except that the strand conductors lie in four separate planes one above the other (see Fig. 4).

As has been previously brought out, it is highly desirable that all of the strand conductors of the wire assembly be essentially coplanar, so that the beam electrons passing between the strands can be properly focused on the desired areas of the base plate 26. In order to establish such a coplanar relationship of the wires, those strand conductors which constitute two sets, such as 44 and 50, are compressed, or forced into a position in which they are not only coplanar with the two sets of conducting strands 46 and 52 but also so that they are interleaved with the latter. Thus the wires of the set 44, for example, will alternate with the wires of the set 46, and the wires of the set 50 will alternate with the wires of the set 52, as again best seen from a consideration of Fig. 3. However, not only do the Wires of one set interleave with the wires of the other set associated with the same winding, but also the wires of one winding are interleaved with the Wires of the other winding. Thus, the final result is a grid Wire assembly such as best shown in the right hand portion of Fig. 3, in which adjacent wires are electrically insulated from one another and alternate wires adapted to have the same electrical potentials applied thereto.

One manner of bringing about a coplanar relationship of all the wires is illustrated especially in Fig. 5 and comprises in part two pairs of metallic wire-aligning bars 54, 56, 58 and 60, each bar having an insert along its lower edge of some electrically-insulative material such as glass. This insert may comprise a ceramic rod, as indicated in the drawing by the reference numerals 54a, 56a, 58a and 60a (Fig. 5). These wire-aligning bars 54, 56, 58 and 60 are secured to, and carried by, the side members 32 of the frame 30, as best shown in Figs. 2 and 3 of the drawings. They are so designed that when they are respectively secured to the side members 32 by the angles or brackets 62 (one of which is shown in Fig. 3 and which is riveted both to its respective wire-aligning bar and to the side member 32) the lower edge of the glass insert carried by the wire-aligning bar is substantially coextensive with the strand conductors which it is designed to align. In other words, a consideration of Fig. 5 of the drawings will show that when the bars 54 and 58 are brought into position (following the formation of the four sets of wire strands as set forth above), then positioning of these bars 54 and 58 will force the two sets of strand conductors 44 and 50 into a position, again best shown in Fig. 5, where they are substantially coplanar with one another. Similarly, positioning of the two wire-aligning bars 56 and 60 will exert pressure upon the two sets of strand conductors 46 and 52 and bring these two sets of conductors into a position in which they are substantially coplanar not only with respect to each other but also with respect to the two sets of strand conductors 44 and 50. Thus a structure is obtained as shown in Fig. 5, in which all four sets of strand conductors are maintained by the wire-aligning bars 54, 56, 58 and 60 in an optimum position for application of selected potentials thereto to produce a focusing and micro-deflection of the cathode-ray scanning beam.

The two wire-aligning bars 54 and 58 are carried on the upper surface. of the frame members 32 (as viewed in Fig. 3, for example) while the two wire-aligning bars 56 and 60 are carried on the lower surface of these two frame members in such a manner that they are oppositelydisposed to the upper two wire-aligning bars. Thus, the assembly above described may be fabricated as a unit, and the coplanar relationship of all of the strand conductors established prior to association of the grid wire assembly with the glass face plate unit in a manner now to be set forth.

The light-transmissive backing, or base plate, 26 carries on one of its surfaces a series of phosphor strips laid down in a manner such as will be described in connection with Fig. 6. That is, the sequence of those phosphor strips may be, for example, red, green, blue, green, red, green, and so on. For proper operation of the tube being described, it is desirable that each of the strand conductors of the grid (which have been brought into coplanar relationship in a manner previously set forth) be aligned in an electro-optical sense with the red and blue phosphor strips. To bring this about, a pair of insulating spacer elements, or bars, 62 are securely afiixed to one surface of the base plate 26 in a manner best shown in Figs. 2 and 5. These spacer bars, as well as the base plate 26, may comprise boro-silicate glass, but in any event should have the same coefiicient of expansion. These spacer bars 62 perform the dual function of aligning the coplanar wire strands of the grid with the phosphor strips and also maintaining the wire strands at a uniform distance from the surface of the base plate 26.

The base plate 26, with its pair of spacer bars 62, is mounted in a pair of L-shaped support members 64 (shown in Fig. 5). The plate 26 is cradled in each L shaped member 64 in the manner shown, the latter members being preferably composed of the same material as the frame sections 32 and 34. A bracket, or angle, 66 at each corner of the frame section 30 (one being shown in Fig. 3) acts to hold the base plate support members 64 in position. When the base plate 26 is secured to the frame section 30 by the angles 66, the sets of wire strands 44, 46, 50 and 52 respectively fall within grooves in the upper surface of the spacer bars 62, these grooves being equally spaced apart :so as to further align and position the individual stnand conductors over and above the positioning effected by the two Winding operations above described. The upper edges of the spacer bars 62 contact the coplanar wires of the grid assembly with just enough pressure to maintain the conductors properly indexed within the grooves or notches cut into the upper surface of these bars.

It will now 'be seen that the grid wires associated with the first winding operation are effectively insulated electrically from those wires associated with the second winding operation. This is brought about, as above described, by three separate mediathe insulating strip, or layer, 48 wound around the frame members 34, the glass inserts 54a, 56a, 58a and 60a within their respective wire-aligning bans, and the insulating spacer bars 62 which serve to index and position each of the individual strand conductors. Since each of these three structures is non-conductive to electricity, separate potentials may be applied to the strands of the two windings so as to provide the desired micro-deflection of the cathode'ray beam.

The relative position of the conducting strands, or grid wires, and the red, green and blue phosphor strips which are applied to that surface of the base plate 26 impacted by the electron scanning beam is shown in Fig. 6. Although \this particular arrangement of phosphor strips forms no part of the present invention, nonetheless a desirable arrangement has been shown to consist of a sequence of strips such as red, green, blue, green, red, green, and so on. The strips widths are chosen in accordance with tube design so as to provide electro-op'tical rather than physical relationships between the grid wires and the phosphor strips. Each adjacent pair of grid i wires is accordingly designed to sub-tend (in an electrooptical sense) a portion of the target electrode surface which includes phosphor areas of each of the component colors. Generally speaking, however, it may be said that the distance between adjacent grid wires is substan tially equal in one dimension to a single elemental area of the image to be resolved by the cathode-ray tube.

Having thus described the invention, what is claimed is:

1. In a grid structure designed for incorporation into a cathode-ray tube adapted to reconstitute images in a plurality of colors, the combination of a substantially rectangular frame defining a window area, a first continuous conductor wound in coil-like fashion around oppositely-disposed sections of said frame so as to form two sets of substantially parallel strands across the said window area which lie in diiferent planes, a layer of insulating material overlying those portions of said first conductor which encircle .the two said oppositely-disposed frame sections, a second continuous conductor wound in coil-like fashion around said frame so as to overlie said insulating layer, thus forming two further sets of substantially parallel strands across said window area which lie in planes different from those of the first-mentioned sets and means for bringing the strands of all the said sets into substnatially coplanar relationship across the window area of said frame.

2. The combination of claim 1, in which the strand conductors of one group are oiiset from the strand conductors of the other group in such a manner as :to be substantially equally spaced apart when in the said coplanar relationship.

3. The combination of claim 1, in which the said lastmentioned means comprises two pairs of rigid bars positioned to compress said strands into the said coplanar relationship.

4. The combination of claim 3, in which the said bars have inserts of non-conducting material which contact the said strands and hence isolate those formed by the first continuous conductor from those formed by the said second continuous conductor.

5. The method of fabricating a grid structure designed for incorporation into a cathode-ray tube adapted to reconstitute images in a plurality of colors which includes the steps of winding a first wire around a frame in a continuous uninterrupted motion so as to produce two sets of substantially parallel strands respectively lying in planes which are separate yet parallel to one another", applying a layer of insulation over that portion of said frame contacted by said wire, winding a second wire around said frame and over said layer of insulation also in a continuous uninterrupted motion so as to produce two further sets of substantially parallel strands lying in planes which are separate yet parallel to .one another, with the strand conductors of said first two sets being parallel to the strand conductors of the said second :two sets, and then applying pressure to the strands of all of the sets so as to cause such strands to respectively assume positions wherein the strands of both sets are essentially coplanar with the strands of one set interleaved with the strands of the other.

6. A color grid structure for a cathode-ray tube comprising a firame having a pair of side members separated to define borders of a window area, a first conductor tautly wound about each of the side members and spanning the space therebetween normally to be stretched in two adjacent parallel planes, an insulating layer covering the portion of the said first conductor wound about each side member, a second conductor taultly wound about the side members and rested thereon against the insulating layer and also adapted to be stretched in two adjacent planes parallel to the planes of the first conductor and located outwardly therefrom by a distance corresponding to the thickness of the insulating layer, and clamping means having insulating contact elements located adjacent to each side member Within the region of the window spanned by the conductors for shirfting the spaced and tautly stretched parallel conductors normally tending to arrange themselves in four planes into a single common plane with adjacent conductors electrically insulated.

References Cited in the file of this patent UNITED STATES PATENTS 1,492,000 Round Apr. 29, 1924 2,026,725 Baker Jan. 7, 1936 2,446,791 Schroeder Aug. 10, 1948 2,461,515 Bronwell Feb. 15. 1949 2,535,307 Mankin et a l. Dec. 26, 1950 2,568,448 Hansen Sept. 18, 1951 2,590,764 Forgue Mar. 25, 1952 

